Power injectors and mechanically assisted infusion systems for controllably dispensing therapeutically active medications are well known in the art. Typically, such devices include an automatic injector for syringes containing an injectable liquid and a plunger or piston movable within the barrel of the syringe to expel said liquid through a tip thereof and injecting into a patient via a tubing connected to an injecting needle or catheter. For controlling the injections parameters, the plunger is driven by means of an electromechanical arrangement organised to push the plunger at a desired rate, continuously or at chosen intervals, so that the amount of medication is delivered to the patient's body under strictly determined conditions. For instance, in the case of intravenous dispensing contrast agent formulations for diagnostic purposes (X-ray, MRI or ultrasound), the rate and the mode of injection can be accurately controlled to match the requirements of the imaging methods and detector systems used to investigate the circulation or a specific organ in the body. Typical automated injection devices are illustrated and described in U.S. Pat. No. 5,176,646 incorporated herein by reference.
Although the automated injectors known are highly sophisticated instruments capable of mastering most injection problems experienced in practice, there remains at least one variable factor not yet under control. Indeed the known power injectors have no control of the homogeneity of the liquid stored within the syringe barrel during the course of its application. This kind of problem is of course non-existent with “true solutions” (i.e. solutions to the molecular level) since in this case no concentration change can occur in the course of time; it however may become important when the injectable formulation is a suspension or dispersion of active particles which tend to settle, coalesce or segregate with time in the syringe. Indeed, even some modest separation of the particles by gravity or otherwise from the carrier liquid in the course of administration of the formulation may have very important influence on reproducibility and reliability of the tests. Hence, in this case, a method and means to keep the syringe content homogeneous during injection is highly desirable. The present method and device constitute a very effective solution to the aforediscussed problem.